Toy submarines are typically used by children in bathtubs and swimming pools. Toy submarines have been available in two varieties. One type is self-propelled and the other is not self-propelled. The self-propelled types are powered either by floatation, chemical reaction, battery, or a windup mechanism.
Floatation powered designs are generally made in such a configuration that they are lighter than the water they displace. When the submarine is released at below the water surface, as the submarine moves towards the water surface it will be propelled forwards depending on the shape and weight distribution of the toy. One of the problems with these designs is that in order for the submarine to move forward, it must be released at depth. That means that the potential forward movement in a bathtub is small and in a pool, a small child can only submerge the submarine to a shallow depth. Also, this design is incapable of self-propelled descending motion or self-propelled constant depth motion. Children can become easily bored with these designs.
Chemical reaction powered designs are generally configured to be slightly negatively buoyant. When a tablet of a chemical such as common baking soda is placed inside of a compartment in the submarine, as water reacts with the baking soda, gas is produced which is captured such that the buoyancy of the submarine becomes positive. When the buoyancy becomes positive, the submarine will climb to the surface. These designs share the same problems as floatation powered submarines and additionally have the cost and hassle and complexity of requiring an expendable chemical. Also, the motion is relatively slow.
Battery powered designs are usually neutrally buoyant and generally have a small battery powered motor with a single propeller. With a single propeller turning, there is a tendency for the submarine to rotate in the opposite direction of the propeller. In order to combat this tendency, the propeller is relatively small and the submarine is weighted such that the submarine will tend to remain in a generally upright orientation. In actual use, these submarines twist at an odd angle in response to the motor-driven propeller. Battery powered submarines move very slowly because of the relatively small propeller and in order to prevent the submarine from twisting at too great of an angle. If too much power were introduced to the propeller, then the submarine would begin to rotate repeatedly in the direction opposite to the propeller. While in theory it would be possible to use a counter-rotating propeller system to solve some of the above problems, in reality this would add too much complexity and cost for a simple toy. Some battery-powered designs also include a chemical reaction system for surfacing.
Existing wind-up powered designs are similar to battery powered designs except that they use a wind-up mechanism instead of a battery and motor. The wind-up mechanism usually includes a metal spring, small gears and a knob for the child to twist in order to create the potential energy. The problem with these designs is that the distance traveled is small because the wind up mechanism allows relatively few windings, the motion is slow, and the buoyancy is such that the "submarine" is really more like a "boat". Also, the motion is not in a straight line.
It is desirable for the toy submarine to be simple to use and operate even for very young children. It is also desirable for the toy submarine to be inexpensive and easy to manufacture. It is also desirable for the toy submarine to not contain any small, sharp components so that it is safe for very young children. It is also desirable for the toy submarine to move through the water in a relatively straight line. It is also desirable for the toy submarine to require little or no maintenance. It is also desirable for the toy submarine to be able to move across swimming pools after being wound up.